1. Field of the Invention
Various techniques are used for the thermal control of space vehicles, namely active control or passive control.
2. Description of the Prior Art
Active control uses thermal machines or systems for transferring thermal energy from one point to another. Passive control uses coating materials which have well-defined thermooptical properties, such as the solar absorption coefficient .alpha..sub.s and the infrared emissivity factor .epsilon..
Three categories of coating materials may be distinguished:
cold coating materials: low .alpha., high .epsilon.: .alpha..sub.s /.epsilon.&lt;(e.g. white paints, SSM, OSR); PA1 moderate temperature coating materials: .alpha..sub.s.apprxeq..epsilon..apprxeq.0.3, .alpha..sub.s /.epsilon..apprxeq.1 (e.g. aluminum paints, metals); PA1 hot coating materials: high .alpha..sub.s, high .epsilon. with .alpha./.epsilon.&gt;1 (e.g. black paints, solar absorbers). PA1 in respect of the solar absorption factor, by the deposited metal (aluminum, .alpha..sub.s.apprxeq.0.10; silver, .alpha..sub.s.apprxeq.0.08); the more transparent the quartz or polymeric film, the better the solar absorption; PA1 in respect of the infrared emissivity, by the polymeric film or the quartz tile; in the case of the polymeric film, the emissivity depends on the thickness e (for example, in the case of Teflon.RTM. FEP, .apprxeq.=0.48 for e =25 .mu.m and .epsilon. 0.75 for e=125 .mu.m). PA1 1) using polysiloxanes having two-dimensional or three-dimensional structures and comprising radicals which either can coreact mutually, or can be crosslinked with polydimethylsiloxanes to create linear chains between the two-dimensional or three-dimensional blocks; PA1 2) from a polysiloxane of formula ##STR5## PA1 self-crosslinking two-dimensional ##STR6## PA1 crosslinking with polydimethylsiloxanes: two-dimensional ##STR7## PA1 self-crosslinking ##STR8## PA1 polysilesesquioxances of the type ##STR9## PA1 polysiloxanes having a three-dimensional structure of the type: ##STR10## PA1 polydimethylsiloxanes having reactive groups at the ends of the chain, such as : --H, --CH.dbd.CH.sub.2, --OH, --Cl, --Br, --O-Me, --O-Et, --O--Ac, --N--Me.sub.2, --O--N.dbd.CR.sub.2, etc. PA1 polydiethoxysiloxane, polydimethoxysiloxane PA1 polydimethylsiloxanes having reactive groups at the ends of the chain or in the chain, such as : --H, --CH.dbd.CH.sub.2, --OH, --Cl, --Br, --O-Me, --O-Et, --O--Ac, --N-Me.sub.2, --O--N.dbd.CR.sub.2, etc.; PA1 a crosslinking agent such as : dimethyldiacetoxy-silane, vinylmethyldiacetoxysilane, ethyltriacetoxy-silane, methyltriacetoxysilane, vinyltriacetoxysilane, silicon tetraacetate, dimethyldiethoxysilane, 1,1,3,3-tetramethyl-1, 3-diethoxydisiloxane, methyltriethoxy-silane, methyltrimethoxysilane, dimethyltetramethoxy-disiloxane, tetraethoxysilane, tetramethoxysilane, tetra-propoxysilane, bis(N-methylbenzylamido)ethoxymethyl-silane, bis(dimethylamino)dimethylsilane, bis(dimethyl-amino)methylvinylsilane. PA1 tin salts such as: dibutyltin diacetate, dibutyltin dilaurate, tin octoate, dibutyltin dioctoate, tetrabutyltin, dimethoxydibutyltin, etc.; PA1 zinc salts: zinc octoate, zinc acetate, etc.; PA1 titanium compounds: tetrabutylitatanate, tetra-ethylititanate titanate, tetraoctyl titanate, tetramethylit-tanate, tetra-n-propylititanate, etc.; PA1 complexes of platinum with divinyltetra-methyldisiloxane, cyclovinylmethylsiloxane, etc.
With regard to cold coating materials, SSM (Second Surface Mirror) materials consist of a metallized polymeric film and OSR (Optical Surface Reflector) materials consist of a metallized quartz or glass tile.
SSM polymeric films usually consist of Teflon.RTM. FEP (a tetrafluoroethylene-hexafluoropropylene copolymer), Mylar.RTM. (polyester) or Kapton.RTM. (polyimide), all from Du Pont de Nemours, which are metallized using aluminum or silver. The highest performance SSMs are of the Al/Teflon.RTM. FEP or Ag/Teflon.RTM. FEP type. OSRs usually consist of a metallized tile, 100 micrometers thick, of very pure quartz or cerium-doped glass.
The thermooptical properties of SSMs and OSRs are imparted:
The mass per unit area of SSMs and OSRs is high, given the density of Teflon.RTM. FEP (d=2.24) in the case of SSMs and of quartz (d=2.20) in the case of OSRs. The cost of these materials is very high, especially in the case of OSRs, since the vacuum deposition of metal can only be carried out on small areas (typically 5.times.5 cm).
If these coating materials are applied to a spacecraft, there is additionally the cost of placing (by bonding) the SSMs and OSRs (use of very expensive special tools).
There is therefore a need for high-performance thermal control coating materials which are lighter and less expensive than the current coating materials.
The invention aims to satisfy this need.